In kinescope displays drawn from computer memory that describe graphics, the practice is to sample both the luminosity and the chromaticity of the same picture elements ("pixels"). This is done to maintain high resolution edges in chrominance signal components as well as in luminance signal components. Since luminance and chrominance are sampled with equal spatial densities, the video data is stored in the form of pixel descriptors for successive pixels in raster scan, each descriptor containing both luminance and chrominance information concerning a particular pixel. These descriptors may be stored in a bit-map-organized format or in a run-length format, for example. These pixel descriptors may comprise luminance and chrominance signal components per se. But often these pixel descriptors are pointer data applied as read addresses to color map memories that store luminance and chrominance signal components in their addressed storage locations.
In kinescope displays based on camera-originated video, a practice has been to use narrower spatial bandwidths for chrominance than for luminance. A computer memory for storing such video in digital sampled-data form may sample luminance signal more densely than chrominance signal in the direction of line advance in the raster scan as well as in the direction of pixel scanning along a raster line. In effect, then, one chrominance pixel takes up the same area on the display screen as a rectangular array of smaller-area luminance pixels. Such systems particularly well-suited to storing luminance and chrominance data in a video random-access memory (VRAM) with serial output port are described in detail by D. L. Sprague, N. Fedele and L. D. Ryan in U.S. Pat. No. 4,740,832, filed Oct. 14. 1986, entitled "IMAGE STORAGE USING SEPARATELY SCANNED LUMINANCE AND CHROMINANCE VARIABLES" and assigned to RCA Corporation. In these systems, to accommodate the difference in luminance and chrominance signal sampling densities, luminance and chrominance are stored in separate bit-map-organized portions of the video random-access memory. The samples of luminance signal are read from VRAM serial output port on a real-time basis during line trace intervals. The samples of chrominance signal are read from VRAM serial output port on a compressed-and-advanced-in-time basis during line retrace intervals. The chrominance signal is retimed and is resampled in an interpolation process supported by rate-buffering line stores, to generate a new set of chrominance samples in suitable temporal relationship with related luminance samples.